I started with 5.5 gallons in a 12 gallon 16" high 14" diameter SS pot...I ended up with about 3.5 gallons after a vigorous 1 hour boil. I don't use a lid but I've never experienced this problem before...I figure I had the burner up too high and it boiled off too much but when I programmed the recipe into BTP it said I would end up with 5.1 gallons after 1 hour...any help is appreciated.

BTP can only predict the boil-off based on the evaporation rate you've entered. My boil-off from a similar diameter pot is 1.25 gallons/hr from a restrained boil and I've hit 1.5 gallons with a vigorous boil an a dry day.

I usually tell people to start with about 6.75 gallons preboil. This should get most to about 5.5 gallons post-boil, ~5.25 gallons post transfer to fermentor and ~5 gallons by the time you get to the keg or bottling bucket. I've never heard of anyone who could start with 5.5 gallons and end with 5 gallons.

You may need to turn the heat down or start with 7 gallons. On a brighter note, it should help your efficiency.